DESCRIPTION: Dr. Picker proposes to develop two new assays for quantitating recent thymic emigrants in humans, the detection of T cell receptor rearrangement excision circles and the use of multiparameter flow cytometry to detect unique cell surface phenotypes. The first assay measures very common TC rearrangement-generated episomal circles from the TCR-delta rec locus to pseudo-J-alpha region, and the second assay measures CD8+ T cells that are CD103+, CD27 bright, CD95 dim, CD45RA+/RO-, Cdlla dim, and CD62L bright. When these assays are standardized, they will be applied to patients on HAART to monitor the level of thymic output of naiDve T cells.